1. Technical Field of the Invention
The present invention relates generally to a fuel injection control system equipped with a fuel accumulator and a fuel injector working to inject fuel supplied from the fuel accumulator, and more particularly to such a system designed to ensure the steady balance between amounts of fuel fed to and discharged from the accumulator.
2. Background Art
There are known common rail fuel injection systems for diesel engines of automotive vehicles which are equipped with a controller, a common rail, and a fuel pump. For example, Japanese Patent First Publication No. 62-258160 discloses a typical common rail injection system. The common rail injection system is typically designed to determine a target pressure of fuel in the common rail depending upon operating conditions of an engine to change the pressure of fuel to be supplied to fuel injectors.
The common rail injection system usually works to control the feeding of fuel from the fuel pump to the common rail to bring the pressure in the common rail, as measured by a fuel pressure sensor, into agreement with the target value under feedback control. For instance, the system calculates a proportional term and an integral term in a PI algorithm based on the pressure in the common rail and the target pressure to determine a target amount of fuel to be discharged by the fuel pump and converts it into an electric current for driving the fuel pump to feed the target amount of the fuel to the common rail to bring the pressure into agreement with the target value.
In the case of use in a synchronous mode to synchronize the feeding of the fuel to the common rail with each injection of the fuel into the engine, the common rail fuel injection system is required to feed the amount of fuel to the common rail which compensates for the amount of fuel consumed by injection into the engine to ensure steady balance between the amounts of fuel flowing into and out of the common rail.
If, however, a failure has occurred in energizing one(s) of fuel injectors due to, for example, a disconnection of an injector's power supply line or one(s) of the fuel injectors encounters mechanical or electrical trouble in itself, it will result in instability in synchronization of the feeding of fuel to the common rail with the injection of fuel into the engine, thus leading to an unbalance between the amounts of fuel flowing into and out of the common rail. This results in an increased variation in pressure of the fuel in the common rail and lowered controllability of the pressure in the common rail.